1. Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method and an apparatus of mapping a resource unit.
2. Related Art
Wireless communication systems are widely spread all over the world to provide various types of communication services such as voice or data. In general, the wireless communication system is a multiple access system capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth, transmit power, etc.). Examples of the multiple access system include a code division multiple access (CDMA) system, a frequency division multiple access (FDMA) system, a time division multiple access (TDMA) system, an orthogonal frequency division multiple access (OFDMA) system, a single carrier frequency division multiple access (SC-FDMA) system, etc.
The institute of electrical and electronics engineers (IEEE) 802.16 standard provides a technique and protocol for the support of broadband wireless access. The standardization had been conducted since 1999 until the IEEE 802.16-2001 was approved in 2001. The IEEE 802.16-2001 is based on a physical layer of a single carrier (SC) called ‘WirelessMAN-SC’. The IEEE 802.16a standard was approved in 2003. In the IEEE 802.16a standard, ‘WirelessMAN-OFDM’ and ‘WirelessMAN-OFDMA’ are further added to the physical layer in addition to the ‘WirelessMAN-SC’. After completion of the IEEE 802.16a standard, the revised IEEE 802.16-2004 standard was approved in 2004. To correct bugs and errors of the IEEE 802.16-2004 standard, the IEEE 802.16-2004/Cor1 was completed in 2005 in a format of ‘corrigendum’. A standard based on the IEEE 802.16-2004/Cor1 is referred to as IEEE 802.16e or WiMAX.
In the IEEE 802.16 broadband wireless access working group, there is ongoing standardization effort for the IEEE 802.16m standard which is a new technical standard based on the IEEE 802.16e. The IEEE 802.16e system uses a time division duplex (TDD) scheme in which a downlink (DL) and an uplink (UL) are temporally divided, whereas the IEEE 802.16m is expected to use not only the TDD scheme but also a frequency division duplex (FDD) scheme in which the DL and the UL are spectrally divided. Furthermore, in order to improve a transfer rate, a frame of the IEEE 802.16m system is designed by considering bandwidth expansion, decrease in a cyclic prefix (CP) size, transmission in a subframe unit in which a frame is divided into a plurality of subframes, mapping of a resource unit in a multi-cell environment, etc.
A resource unit is classified into a physical resource unit (PRU) and a logical resource unit (LRU). The PRU is a basic physical unit for allocating resources including a plurality of contiguous subcarriers ? a plurality of contiguous orthogonal frequency division multiplexing (OFDM) symbols. The LRU is a basic logical unit for allocating distributed and localized resources.
Meanwhile, in a frequency domain, the resource unit may be spread along a frequency axis according to a predetermined permutation rule which is designed to obtain a frequency diversity gain. Permutation implies mapping of one set of resource units onto same-sized another set of resource units. Mapping of a resource unit is a method in which a PRU is mapped to a contiguous resource unit (CRU) and a distributed resource unit (DRU) in the frequency domain and the CRU and the DRU are allocated to a cell (or sector) specific resource by dividing the CRU and the DRU into one or more frequency partitions. Alternatively, permutation may imply an operation of allocating an index of the PRU to an index of the LRU. In this case, each index can be allocated one time. Permutation can be performed in a resource unit having a specific granularity. The less the size of the granularity, the greater the frequency diversity gain resulted from permutation.
Hereinafter, contiguous PRUs will be referred to as a PRU set or a subband. One subband includes a plurality of contiguous PRUs in the frequency domain, and is suitable for frequency selective allocation. A frequency band corresponding to one subband can be allocated to an optimal frequency channel for a user equipment. For example, one subband may include 4 contiguous PRUs. A miniband includes a less number of PRUs than the subband, and is permutated in the frequency domain. The miniband is suitable for frequency division allocation. For example, one miniband may consist of one PRU.